Macrophages and related cells of the reticuloendothelial system play essential roles in host defense mechanisms against infectious disease and neoplasia. Abnormalities in macrophage development and function are implicated in the pathogenesis of a wide variety of human disease states, including certain leukemias, autoimmune diseases and atherosclerosis. The long term objectives of this proposal are to elucidate the molecular mechanisms by which receptors for retinoic acid and Vitamin D regulate macrophage development. AIM 1 proposes to identify retinoic acid and Vitamin D-responsive genes in the human leukemia cell line, HL60, using subtractive hybridization strategies. These studies are expected to lead to the identification of genes that play important roles in the development and terminal differentiation of hematopoietic cells. Furthermore, characterization of the transcriptional control of these genes will be a prerequisite to the understanding of the mechanisms by which retinoic acid and Vitamin D exert tissue-specific effects on gene expression. Biochemical studies of HL60 cell nuclear proteins have led to the identification of two cell-specific factors that interact with the retinoic acid receptor to alter its sequence-specific DNA binding properties. The major hypothesis raised by this proposal is that these factors act to restrict and direct the actions of the retinoic acid receptor to the appropriate sets of target genes in hematopoietic cells. AIM 2 proposes to characterize and clone these factors in order to test this hypothesis. The retinoic acid receptor interacts with these cell-specific factors via amino acid sequences that overlap with domains involved in ligand binding and transcriptional activation. AIM 3 proposes to perform a mutational analysis of this protein-protein interaction interface in order to understand the relationship between these interactions and the transcriptional properties of the receptor. The proposed studies are likely to provide new insights into the mechanisms by which the retinoic acid and Vitamin D receptors influence the hierarchy of regulatory genes that act to specific cellular phenotype and control cell growth.